Light Up The World

[**DONOTDELETE**]

Hi Folks,
I would truly appreciate some help in designing a sort of "universal reference circuit" for our LUTW initiative. We have designs in hand but are not convinced that they are the best that can be achieve with the technology available today.
The LUTW Foundation has, since 1997, been instrumental in taking solid state (White LED) home lighting to the developing world.
Our lamps consist of a single Luxeon and a home might have from one to three lamps. The batteries used will vary from a set of three rechargeable "D" cells, to 6 Volt and 12 Volt Sealed Lead Acid. As we operate in very remote areas of the world where electrical energy is a scarce commodity it is absolutely essential that we squeeze every last Joule out of the batteries (when necessary). In other words the constant current DC-DC converter circuit MUST use the battery energy very efficiently whilst being as simple and economic to manufacture in the developing country as possible. The one to three Luxeon lamps will operate from a single battery so the on/off switching circuit might influence the overall efficiency.
If you are interested in assisting us then please have a look at our web site to learn a wee bit more about LUTW.

www.lightuptheworld.org

Take care and thank you in advance for your help.
Namaste,
Dave.

 

[lightlover]

That must be Dave Irvine-Halliday, Associate Professor of Electrical and Computer Engineering at the University of Calgary.

Prof., I have read of your project, LUTW, and if you want any help or advice regarding LED's and their associated circuits and applications, you're probably in the right place.

I hastily add that I myself can't be much help in that. But I know a few very well qualified members who can.

lightlover

 

[lightlover]

Ummm,
maybe the smart people don't come to the Café forum so much ......

People, this is CPF's chance to help alter the course of history, so to speak.

And you also get to be able to say
"Well, as I advised an Associate Professor of Electrical and Computer Engineering recently ...... ".
Sounds like a great thing to just drop into conversation !!

Prof, I'll move this over to the LED, Electrolumenescent and Lasers Forum.
(That's where all the Electric People hang out.)

lightlover

 

[brightnorm]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Dave Irvine-Halliday:
Hi Folks,I would truly appreciate some help in designing a sort of "universal reference circuit" for our LUTW initiative.
<HR></BLOCKQUOTE>

Dave,

This is clearly a very important and worthwhile project, but your header: "Light Up The World" is unfamiliar to most people and might easily be misconstrued as something frivolous or even humorous.

Please don't think it presumptuous of me when I suggest that changing that header might elicit a broader response.

I'm not sure what title would be appropriate.
Maybe something like: "CPF input needed for University project" or "LED circuit design for universal lighting technology" etc.

Unfortunately I have no expertise in this area, but I know that there are some
"Flashaholics" with very sophisticated knowledge in LED's who might be able to help.

Good luck.

Best regards,
Brightnorm

 

[Lux Luthor]

Brightnorm is right. I almost didn't click on this thread, and only did so because I happened to be bored at the moment. If you edit your original post, you can change the topic title since it is the leading post.

 

[lambda]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Dave Irvine-Halliday:
The batteries used will vary from a set of three rechargeable "D" cells, to 6 Volt and 12 Volt Sealed Lead Acid. As we operate in very remote areas of the world where electrical energy is a scarce commodity it is absolutely essential that we squeeze every last Joule out of the batteries (when necessary). In other words the constant current DC-DC converter circuit MUST use the battery energy very efficiently whilst being as simple and economic to manufacture in the developing country as possible. The one to three Luxeon lamps will operate from a single battery so the on/off switching circuit might influence the overall efficiency.
<HR></BLOCKQUOTE>

The range of 4.5V to 12V, and the simplicity requirement present the biggest challenge, but almost beg for a switch selectable input voltage. To be the most efficient, the power converter would need to be designed for a specific voltage. By switching in/out different components, this might be achieveable.

First, to really help you, we need a little info on what you've already got. You mentioned some desings in hand; we need to know what efficiency your current circuits are achieving. If you're already in the 80 to 90 percent efficiency range, then it becomes more a matter of price and ease of manufacture; somewhere is the optimum efficiency at the optimum price.

Also, you must take into account that squeezing the last joule of energy from a disposable battery is very different from rechargeables like NiMh that don't like being drained to zero volts; they will die quickly. So, here again, different battery types require diiferent circuits for maximum efficiency.

So, if you can tell us little about where you're at with the circuits you have now, and maybe a little more about the actual batteries you envision being used, I'm sure we can all offer some alternatives to choose from.

 

[bikeNomad]

I sent him some email:

I saw your post in the Candlepower forums, and would be willing to help. I've
been designing with the Luxeon LED, and have come up with a couple of
switching converter designs that work well. I am also developing a commercial
product that will use two Luxeons, with a buck converter. I also have some
experience designing systems to do solar charging of SLA batteries (I
developed a small (4A max) microcontroller-based SLA charging unit that also
protected the battery from over-charging; this was for a portable data
acquisition unit (for a NSF project)).

Some questions about your requirements:
<UL TYPE=SQUARE><LI> What are the input and output requirements? Presumably you want a buck
converter (for efficiency reasons) that can run from 2.7V or so (3 D cells)
to 15V (12V SLA with solar charging).
<LI> Do you require variable brightness?
<LI> Do you want to turn off the loads or warn before impending battery damage
(over-discharge)?
<LI> What are your common failure modes? Short circuits? Inductive spikes?
Intermittent wiring? Reversed connections? Corrosion? Static electricity?
<LI> Would it help to have a circuit that could also handle charging of your
batteries? If so, what are the characteristics of the input supplies
(generator/solar?)
<LI> What kind of efficiency do you require?
<LI> What kind of restrictions on parts/manufacturability do you have? Can you
use a microcontroller-based design (these would be in-circuit programmable)?
Surface mount components? What limitations on PCB dimensions? Trace width and
spacing?
<LI> What kind of quantities would you be making?
<LI> What kind of parts lead time could you stand?
<LI> Are the parts going to be purchased in North America or would they have to
be available in Tibet?
[/list]

 

[**DONOTDELETE**]

The ZLT+ DC/DC converter circuit is not only simple and efficient, it's also very inexpensive, especially if Zetex donates the parts.

It would very cool to visit one of these countries and see that circuit in use there

ZLT+ Web Page

Complete ZXSC300 Thread

 

[bikeNomad]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
The ZLT+ DC/DC converter circuit is not only simple and efficient, it's also very inexpensive, especially if Zetex donates the parts.

It would very cool to visit one of these countries and see that circuit in use there

ZLT+ Web Page

Complete ZXSC300 Thread<HR></BLOCKQUOTE>


Except that it's inappropriate for his uses. Remember that he's using either 3 D cells, a 6V, or a 12V battery to run 1-3 Luxeons. So he has to have a step-down converter that can take from 3V-15V inputs.

The step-down (buck) converters are also typically higher efficiency, with 90%+ efficiencies being common.

 

[lightlover]

Guys,
sorry, I forgot to say this a while ago.
Professor Irvine-Halliday is still pursuing this project, but unfortunately, it will be some time before he can get back to you all.

lightlover

 

[yclo]

What about the Versalux Utility Light Module?

YC

 

[Jonathan]

I wonder if this is the sort of project that might convince a semiconductor supplier to design a new chip.

The requirements suggest a buck switching converter, and there are loads of chips available which will do this job.

However since the device is being used for LED drive, you want current feedback. The simplest tool for current feedback is to put a resistor in the current path, and to compare the resistor voltage to a reference voltage. The problem is that the reference voltage used by most of these easily available 1 chip switchers is about 1.25V. Set one of these devices up as a simple current regulator, and you will throw away 25% in efficiency just in the current sense resistor.

I know that there are various tricks that one can use to get a lower reference voltage, but I wonder if it would be possible to select a buck converter chip that is perfect _except_ for the reference voltage, and then convince a manufacturer to build a variant of the chip with a 0.1V reference voltage.

If the chip also had a 'not-shutdown' pin, then a simple resistive divider could be used to make a 'low battery' shutoff.

The entire circuit would then be a switcher chip, an input capacitor, a pair of resistors for battery sensing, an inductor, the output diode, an output capacitor, the LS diode, and the current sense resistor. The entire circuit would be small, even with through-hole parts.

Another thing to consider: what is the meaning of the requirement that the device be easily assembled anywhere in the world? Clearly components such as the Luxeon LEDs are not being made in someone's back yard. Why not build more of the system in a mass production facility?

Specifically, it might be better to specify a module, which includes the LED and the driver circuitry. The drive circuitry would be designed to operate over a range of voltages, with reverse connection protection, battery cut-off sensing, etc. With SMT components, the entire driver circuit could be mounted on the same metal core PCB that the LED is mounted upon.

This LED module (black box just doesn't cut it for an LED

would then be assembled into a fixture with batteries, switches, bolted to a heat sink, etc. But the LED and its driver components would be potted, protected SMT devices. I'd bet that such a module would not add too much cost to the Luxeon itself, and would be far cheaper than using through hole components on a larger PCB that is then hand assembled.

Regards,
Jonathan Edelson

 

[EMPOWERTORCH]

What a brilliant idea!
Most of Africa's houses are lit by traditional flame light sources such as oil lamps and candles, with thier inherent dangers. I'm just in the beginning of setting up EMPOWERTORCH as a small commercial concern to support the Christian Rock Band EMPOWERED. I'm planning to produce small, simple torches using cyan Nichia LED's and simple resistive regulation. Being mounted in a square box, I might see if I can attach a solarcell to one or more faces of torch case to produce a solar-rechargeable unit. During the day the torch could simply be left in the daylight and at night be used in the conventional way. Such torches could be fully sealed instruments which would make them very rugged and practical, and the solar cells would mean that the torches would cost absolutely nothing to run. LED's, in particular cyan ones, are very efficient and a day's charge under African sun will more than adequately power the instrument for normal handlamp usage. There would be no flames, no wires to trip over and a very portable handheld light source.
At present I'm at the very start of my venture building dry cell powered devices and torch conversions using Nichia 5mm LED's.
These seem to be able to squeeze the last joules out of virtually dead batteries and give ueable light. I've tested Nichia green LED's and they give useable light right down to 1 mA! This typically would barely light most filament bulbs if at all!
I've also spotted another light on this forum which could serve you...the "shaker torch" requires no batteries amnd is powered by shaking it! It could be loosely referred to as a "human powered torch" or HPT for short.
Such devices such as mentionned above could radically improve the lives and safety of people in developing and third world countries. EMPOWERED would love to get involved with these projects in the future...